1. Field of the Invention
The present invention relates to an inkjet head for ejecting ink onto a record medium to print, and also to a manufacturing method of the inkjet head.
2. Description of Related Art
An inkjet head used in an inkjet printer includes therein an ink tank and pressure chambers. Each pressure chamber is supplied with ink from the ink tank. When a piezoelectric element provided above a pressure chamber is deformed to change the volume of the pressure chamber, pressure is applied to ink in the pressure chamber so that the ink is ejected through a nozzle connected to the pressure chamber. To deform the piezoelectric element, in general, a driving signal is supplied to a surface electrode provided on a face of the piezoelectric element opposite to the pressure chamber. An electric field is thereby applied to the piezoelectric element. The surface electrode is connected to a terminal on a printed circuit board such as a flexible printed circuit (FPC). The driving signal is supplied to the surface electrode through the printed circuit board from a driver IC connected to the printed circuit board.
In general, electrical connection between the terminal of the printed circuit board and the surface electrode is realized in the manner that solder interposed between the terminal and surface electrode is melted with heat (see JP-A-7-1566376). Besides, there is known a method using no solder (see JP-A-8-156252). In the method using no solder, a printed circuit board is prepared on which two films are put in layers. The lower film has a cut-out portion larger in area than the surface electrode. A terminal smaller in area than the surface electrode is provided on the lower face of the upper film within the cut-out portion of the lower film. After a conductive adhesive is dropped on the surface electrode, the terminal is pressed onto the surface electrode so that they are electrically connected to each other. The connecting portion between the terminal and the surface electrode is at a position opposite to a pressure chamber.
In the above technique using solder for electrically connecting the terminal of the printed circuit board and the surface electrode to each other, however, the solder having melted with heat to have high fluidity may move into a region on the surface electrode opposite to the pressure chamber. In this case, deformation of a piezoelectric element upon ink ejection may be hindered due to the rigidity of the solder. This causes deterioration of ink ejection performance. To avoid this, for example, such a measure is taken as elongating distances between neighboring connecting portions of the terminal and the surface electrode, however, this is contrary to high integration. Furthermore, in case the surface electrode is made of metal, the surface electrode is easily diffused into solder when the solder adheres to a surface electrode. This may cause rise of the resistance between the surface electrode and the terminal, and at worst, electrical braking may happen.
In addition, when surface electrodes corresponding to the respective pressure chambers are connected to terminals corresponding to the respective surface electrodes, solder having melted to have high fluidity may cause a short circuit between neighboring connecting portions.
In the above technique using a conductive adhesive in place of solder, because the conductive adhesive is lower in fluidity than solder upon being heated, the conductive adhesive stays within each cut-out portion of the lower film on the printed circuit board. Therefore, the above-described problems with the case of using solder, such as hindrance of deformation of a piezoelectric element, rise of the resistance, braking, and a short circuit, are relieved in comparison. However, because the connecting portion between the terminal and the surface electrode is at a position opposite to a pressure chamber as described above, there is a problem that deformation of a piezoelectric element upon ink ejection is hindered. This makes it difficult to change the volume of the pressure chamber and thus it causes deterioration of ink ejection performance,